DESCRIPTION: The proposal concerns the formation of left-right asymmetry in heart development. How this asymmetry arises is a basic question in developmental biology, which also has important clinical implications. Dr. Yost has published several articles in the field, mainly with an emphasis on the relatively late role of extracellular matrix, specifically, proteoglycans, in regulating left-right asymmetry. The experiments set out in this proposal will extend on these earlier studies, by focusing more on the earlier embryonic events that regulate left-right asymmetry, beginning with the potential role of maternal components, and progressing into gastrulation stages.